Merge branch 'ds/path-walk-2'

Merge branch 'ds/path-walk-2'

"git pack-objects" learns to find delta bases from blobs at the
same path, using the --path-walk API.

* ds/path-walk-2:
  pack-objects: allow --shallow and --path-walk
  path-walk: add new 'edge_aggressive' option
  pack-objects: thread the path-based compression
  pack-objects: refactor path-walk delta phase
  scalar: enable path-walk during push via config
  pack-objects: enable --path-walk via config
  repack: add --path-walk option
  t5538: add tests to confirm deltas in shallow pushes
  pack-objects: introduce GIT_TEST_PACK_PATH_WALK
  p5313: add performance tests for --path-walk
  pack-objects: update usage to match docs
  pack-objects: add --path-walk option
  pack-objects: extract should_attempt_deltas()